Physical pretreatment of food waste for reducing hydrogen-consuming bacteria

Food waste is a complex organic substrate that is also potentially hosting a variety of microbial species. In Malaysia, the large amount of food waste that is available can cause health and environmental issues due to inadequate management that has created problems such as greenhouse gas emission and release of wastewater. The utilization of food waste for value-added products is an attractive solution to reduce the accumulation of food waste, however, demands a pretreatment step to prepare the food waste for a specific production process. One interesting application of food waste is for the production of biohydrogen, which requires food waste to be free from hydrogen-consuming bacteria (HCB). This study aims to investigate the effect of physical pretreatment on food waste and suggest the best pretreatment parameters. Food waste samples were pretreated with heat at 70 °C, 80 °C and 90 °C for 15 and 30 minutes and UV radiation for 10, 15 and 30 minutes before being cultured in aerobic condition. The reduction in aerobic bacteria was measured. Heat pretreatment at 70 °C for 15 and 30 minutes could be considered as the best pretreatment compared to the other since it recorded the highest reducing sugar concentration. Heat pretreatment at 70 °C for 15 and 30 minutes and UV radiation pretreatment for 15 minutes had a bactericidal effect and able to remove HCB. There is a high possibility that bacteria 2, 7 and 8 were hydrogen-producing bacteria (HPB).

126 Porcine in vitro digestion and fermentation characteristics of heat and multi-enzyme pretreated whole stillage

Effects of heat pretreatment (HT) and multi-enzyme predigestion (MP) of whole stillage on porcine in vitro digestibility of DM (IVDDM) and fermentation characteristics of WS were investigated. Four WS samples were obtained from 4 different sources. Half amount of WS from each source was pretreated at 70psi and 160°C for 20 min. Untreated and pretreated WS samples from each source were divided into 4 sub-samples (4 sub-samples of untreated WS per source and 4 sub-samples of pretreated WS per source) to give 32 sub-samples. Four treatments were applied to 32 sub-samples WS (1 untreated or 1 pretreated sub-sample per treatment per sample source). The treatments were WS undigested or pre-digested with 1 of 3 multi-enzymes (MTE1, MTE2, and MTE3). The MTE1 contained xylanase, β-glucanase, cellulase, mannanase, protease, and amylase; MTE2 contained xylanase, α-galactosidase, and celullase; and MTE3 contained xylanase, cellulase, β-glucanase, and mannanase. The 32 sub-samples were subjected to porcine in vitro digestion in 3 cycles of 2 batches (16 sub-samples/batch). Subsequently, residues were subjected to porcine in vitro fermentation for 72 hours, during which accumulated gas production was recorded and modeled to estimate kinetics of gas production. The IVDDM of untreated WS was 73.4%. HT improved (P< 0.05) of WS IVDMM by 8.2 percentage points. MP improved IVDDM of untreated WS and heat-pretreated WS by a means 9.1 and 6.8 percentage points, respectively. However, the magnitude of improvement in IVDDM of pretreated WS due to predigestion was lower (P< 0.05) for MTE3 than that for MTE2 (4.8 vs. 9.0 percentage points), but similar to that for MTE1 (6.7 percentage points). Similar interactions were observed for total gas production. In conclusion, the digestibility of WS was improved by the HT and MP. Combination of HT and MTE2 predigestion was the most effective in improving digestibility of WS.